Oxygen insertion into boroles as a route to 1,2-oxaborines

Abstract

The synthesis of 1,2-oxaborines is accomplished via the reaction of pentaarylboroles with N-methylmorpholine-N-oxide via a 1,1-insertion reaction. The aromatic nature of 1,2-oxaborines was evaluated by computing nuclear independent chemical shift (NICS) values. Collectively, the experimental and computational studies indicate the unsaturated central BOC4 ring has appreciable aromatic character.

Expedient Synthesis of 1,2‐Thiaborines by Means of Sulfur Insertion into Boroles

“…In particular, this chemistry has flourished for boron/nitrogen species, namely 1,2‐azaborines ( A , Figure ) . With respect to boron–oxygen analogues (1,2‐oxaborines, B ), numerous fused polycyclic systems are known, as well as five monocyclic species . Fewer advances have been made for the third row; in fact, the first 1,2‐phosphaborine C was reported only last year .…”

“…Developing the chemistry of 1,2‐thiaborines could provide access to molecules that exhibit properties similar to thiophene, yet exhibit a profile akin to that of benzene. In contemplating the design of a new route to 1,2‐thiaborines, we were attracted to boroles as they have been shown to be effective reagents for the generation of unsaturated boron ring systems of six to eight atoms . The synthesis of 1,2‐thiaborines by means of this route could provide access to a monocyclic species lacking an amino group on boron.…”

Isomerization and rearrangement of boriranes: from chemical rarities to functional materials

“…Due to integration of the boron's empty p z orbital into the π-system of the molecule, these molecules often display substantially different photophysical/chemical properties compared to their carbon congeners such as intense blue to green luminescence (λ em = 400-491 nm, Φ Fl.~5 0-70%) and tunable redox properties [59]. On the other hand, heterocyclic scaffolds that contain N, B, and either S or O, are virtually unknown, with the closest relatives being aza- [60], thia- [61], and oxaborinines [62]. This type of isosterism in aromatic systems has garnered increasing attention due to the potential use of these B,N-or B,Xembedded aromatics in optoelectronic materials and medicinal science [63].…”

Ring expansion reactions of anti-aromatic boroles: a promising synthetic avenue to unsaturated boracycles

“…The bulkier di-tolyl--substituted derivative resulted in insertion of the terminal nitrogen to form 1,2--azaborines 24 and 25 akin to the conversion of Int15 to 23 in the azide mechanism. 23,49,58 Alternatively, N--methylmorpholine--N--oxide (NMMO) proved to be an effective oxygen atom source. Despite the flourishing field of 1,2--azaborine chemistry, an analogous unsaturated 1,2--PBC 4 heterocycle has been elusive.…”

“…Despite the flourishing field of 1,2--azaborine chemistry, an analogous unsaturated 1,2--PBC 4 heterocycle has been elusive. 58 Interestingly, computational analyses indicate that 1,2--oxaborines have aromatic character approaching the magnitude of 1,2--azaborines. The photolysis of [PPh] 5 to generate phosphinidene synthons was exploited for the 1,1--insertion of a PPh fragment into the borole rings of 1 and 28 to furnish 1,2--phosphaborines 29 and 30 (Fig 11).…”